em357: Corrected EM357 support including errata details

Original submitted code had only been tested with em358, but testing with
actual em357 revealed errors that this patch corrects.

Change-Id: I70cf31210de8ed84e3755a56e76261ad200322bb
Signed-off-by: Ed Beroset <beroset@ieee.org>
Reviewed-on: http://openocd.zylin.com/2581
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

tcl/target/em357.cfg

@@ -34,7 +34,7 @@ if { [info exists CPUTAPID] } {
 if { [info exists BSTAPID] } {
    set _BSTAPID $BSTAPID
 } else {
-  set _BSTAPID 0x069aa62b
+  set _BSTAPID 0x069a962b
 }
 
 if { [info exists CHIPNAME] } {
@@ -63,5 +63,14 @@ set _FLASHNAME $_CHIPNAME.flash
 flash bank $_FLASHNAME em357 0x08000000 $_FLASHSIZE 0 0 $_TARGETNAME
 
 if { ![using_hla]} {
-    cortex_m reset_config sysresetreq
+# according to errata, we need to use vectreset rather than sysresetreq to avoid lockup
+# There is a bug in the chip, which means that when using external debuggers the chip
+# may lock up in certain CPU clock modes. Affected modes are operating the CPU at
+# 24MHz derived from the 24MHz crystal, or 12MHz derived from the high frequency RC
+# oscillator. If an external debugger tool asserts SYSRESETREQ, the chip will lock up and
+# require a pin reset or power cycle.
+#
+# for details, refer to:
+# http://www.silabs.com/Support%20Documents/TechnicalDocs/EM35x-Errata.pdf
+    cortex_m reset_config vectreset
 }

tcl/target/em358.cfg

@@ -1,4 +1,3 @@
-#
 # Target configuration for the Silicon Labs EM358 chips
 
 #
@@ -9,6 +8,10 @@ if { ![info exists CHIPNAME] } {
    set CHIPNAME em358
 }
 
+if { ![info exists BSTAPID] } {
+  set BSTAPID 0x069aa62b
+}
+
 # 512K of flash in the em358 chips
 set FLASHSIZE 0x80000
 source [find target/em357.cfg]